| 摘要 |
1520478 Detecting earth leakage THOMSON-BRANDT and LCC CICE COMPAGNIE EUROPEENE DES COMPOSANTS ELECTRONIQUES 22 Oct 1975 [24 Oct 1974 21 Nov 1974] 43452/75 Heading H2K In an electrical apparatus which is fed from an A.C. supply via a conventional differential current transformer responding to earth leakage and which comprises some components, carrying rectified current, which are double insulated from earth and other components, connected to the A.C. supply, which can only be single insulated, the two kinds of components are interconnected by connecting components whose characteristic values are such that should an insulation fault occur in one of the components carrying rectified current, the differential transformer will remain unsaturated and effective to respond to the fault. In Fig. 1 the D.C. motor 23 of a washing machine is supplied from an A.C. source through a differential transformer (not shown), a double pole switch 11 and a rectifier bridge 12 and is regulated by a conventional control circuit 17, 18, 22 ... A programmer 33 includes the switch 11 and switches 34 ... 38 all of which have class I insulation, with the motor and its control circuit components being provided with class II insulation. The latter components are connected to the switches 34 ... 38 through resistors 41 ... 45, whose values are chosen to give a total greater than 10,000 ohms which ensures that an insulation fault in the motor, its control circuit or bridge 12 has no adverse effect on the operational sensitivity of the differential transformer. The resistors may be replaced by capacitors (141 ... 181) having a total capacitance between 10,000 and 100,000 picofarads, Fig. 3 (not shown), which modification includes further resistors, capacitors and balancing diodes (142 ... 182, 145 ... 185, 143 ... 183 and 144 ... 184). The transformer sensitivity is also protected against the harmonics produced by regulation of the motor, since transmission of these harmonics to the A.C. supply is prevented. |
